Functionalized polypropylenes and process for production

ABSTRACT

A novel process for preparing functionalized polypropylenes entailing apportioned introduction of free radical initiator is described. Also described are novel functionalized polypropylenes having a yellowness index color of at least 77 and a Brookfield Thermosel viscosity of greater than 7000 cP at 190° C. Preferably, the functionalized polypropylenes are further characterized by having an acid number greater than 6 milligrams of KOH per gram of polymer.

FIELD OF THE INVENTION

This invention relates to novel functionalized polypropylenes having aunique combination of viscosity and yellowness index properties. Thisinvention also relates to a novel polypropylene functionalizationprocess.

BACKGROUND OF THE INVENTION

Grafting of monomers onto polyolefins is well known (see ‘PolymerChemistry’ by M. P. Stevens, (Addison-Wesley), 1975, pp. 196-202).Maleation for example, is a type of grafting wherein maleic anhydride isgrafted onto the backbone chain of a polymer. Maleation of polyolefinsfalls into at least three subgroups: maleation of polyethylene,maleation of polypropylene, and maleation of copolymers of propylene andethylene or other monomers.

Maleation of polyethylene provides higher molecular weight products witha noticeable decrease in melt index due to cross-linking, unless specialprovisions are made, (see for example “Journal of Applied PolymerScience”, 44, 1941, N. G. Gaylord et al (1992); and U.S. Pat. Nos.4,026,967; 4,028,436; 4,031,062; 4,071,494; 4,218,263; 4,315,863;4,347,341; 4,358,564; 4,376,855; 4,506,056; 4,632,962; 4,780,228;4,987,190; and 5,021,510). Maleation of polypropylene follows anopposite trend and yields lower molecular weight products with a sharpincrease in flow rate due to fragmentation during the maleation process(see for example U.S. Pat. Nos. 3,414,551; 3,480,580; 3,481,910;3,642,722; 3,862,265; 3,932,368; 4,003,874; 4,548,993; and 4,613,679).Some references in the literature fail to note the difference betweenmaleation of polyethylene and polyproplyene, and claim maleation ofpolyolefins with conditions which are useful only for eitherpolyethylene or polypropylene, respectively. In general, conditionswhich maleate polypropylene are not ideal for maleation of polyethylenedue to the opposite nature of the respective maleation chemistries:fragmentation to lower molecular weights for polypropylene andcross-linking to higher molecular weights for polyethylene. This isshown in U.S. Pat. No. 4,404,312. Maleation of copolymers of propyleneand ethylene or other monomers follow the pattern of the majoritycomponent.

Maleations of polypropylene can also be further subdivided into batch orcontinuous processes. In batch processes generally all of the reactantsand products are maintained in the reaction for the entire batchpreparation time. In general, batch maleation processes are difficult touse competitively in commerce due to high cost. Batch processes areinherently more expensive due to startup and cleanup costs.

The maleated polypropylenes that are reported in the previous literaturecan also be divided into two product types as a function of whether ornot solvent is involved, either as a solvent during reaction or inworkup of the maleated products. In U.S. Pat. Nos. 3,414,551; 4,506,056;and 5,001,197 the workup of the product involved dissolving the maleatedpolypropylene product in a solvent followed by precipitation, or washingwith a solvent. This treatment removes soluble components and thusvaries both the ‘apparent’ molecular weight and the acid number.Processes using an extruder produce a product in which solvent solublecomponents remain. In addition, extruder processes often incorporate avacuum system during the latter stages of the process to remove volatilelower molecular weight components. Thus, different compositions arenecessarily present in products produced in an extruder in contrast tothose products from solvent processes or those which use a solvent inproduct workup.

Another subdivision of maleation of polyolefins concerns the state ofthe reaction process. Solvent processes, or processes where solvent isadded to swell the polypropylene (see U.S. Pat. No. 4,370,450), areoften carried out at lower temperatures than molten polyolefin (solventfree) processes. Such processes involve surface maleation only, withsubstantial amounts of polypropylene below the surface being maleationfree. Processes using molten polypropylene involve random maleation ofall of the polypropylene. Solvent processes are also more expensive inthat solvent recovery/purification is necessary. Solvent purification iseven more expensive if the process inherently produces volatileby-products, as in maleation. Note that if water is the ‘solvent’polypropylene is not soluble and reaction must occur only on the surfaceof the polypropylene solid phase. Further, in aqueous processes maleicanhydride reacts with the water to become maleic acid. In these two waysprocesses containing water are necessarily different from non-aqueousprocesses. In a molten process no solvent or water remains at the end ofthe process to be purified or re-used. Thus a molten process would beenvironmentally ‘greener’ and less expensive.

SUMMARY OF THE INVENTION

The composition according to the present invention comprises afunctionalized polypropylene having a yellowness index color of at least77, and a Brookfield Thermosel viscosity of greater than 7000 cP at 190°C. Preferably, the functionalized polypropylene is further characterizedby having an acid number greater than 6 milligrams of KOH per gram ofpolymer.

The novel process according to the present invention for the productionof functionalized polypropylenes, including the novel functionalizedpolypropylenes of the present invention, is comprised as follows. Apolypropylene is introduced into an apparatus, either in premolten formor as solid particulates (for example, pellets or powder) which are thenmelted; into the molten polypropylene is introduced a portion of therequired amount of a free radical initiator, and the moltenpolypropylene and free radical initiator are mixed; into the resultantmixture is then introduced the entire amount of a functionalizing agentwhich is mixed therewith such that the functionalizing agent, theinitial portion of initiator and the polypropylene are reacted; into theresultant reaction mixture is then introduced the remainder of therequired amount of the free radical initiator to thereby form thedesired functionalized polypropylene; and recovering the resultantfunctionalized polypropylene.

The remaining portion of the free radical initiator added after thefunctionalizing agent addition may be carried out in a plurality ofzones. In each case the portion of the remaining free radical initiatoradded is mixed to form an intermediate reaction product into whichadditional free radical initiator is added. The percent of the remainingfree radical initiator that may be added in each of the plurality ofzones is between 1% and 99% by weight of the remaining free radicalinitiator added after the functionalizing agent addition. Preferably,the number of additional free radical initiator injection zones isbetween 2 and 10.

The polypropylene utilized herein has a melt flow rate of preferablyabout 0.1 to about 50 at 230° C. Moreover, the process described hereinmay be practiced in a continuous or batch manner.

DETAILED DESCRIPTION OF THE INVENTION

The applicant has unexpectedly discovered a novel batch or continuousprocess to functionalize polypropylenes. The process may be used toprepare a wide variety of functionalized polypropylenes, some of whichare novel functionalized polypropylenes.

The novel functionalized polypropylenes according to the presentinvention have a yellowness index color of at least 77. The yellownessindex color analysis is illustrated in the examples. The functionalizedpolypropylenes according to the present invention preferably have ayellowness index color ranging from at least 77 to about 200, morepreferably from at least 77 to about 150, with a yellowness index colorfrom at least 77 to about 120 being most preferred. A still furtherpreferred yellowness index color ranges from 81 to about 120.

The functionalized polypropylene of the present invention has aBrookfield Thermosel viscosity of at least 7,000 cP at 190° C. TheBrookfield Thermosel viscosity is preferably at least 7,000 to about100,000 cP at 190° C., with a Brookfield Thermosel viscosity at 190° C.of about 16,000 to about 80,000 cP being most preferred.

The novel functionalized polypropylenes according to the presentinvention are further characterized by preferably having an acid numbergreater than 6 milligrams of KOH per gram of polymer (the method ofdetermining acid number is illustrated in the examples). Thefunctionalized polypropylenes according to the present invention morepreferably have an acid number ranging from greater than 6 milligrams ofKOH per gram of polymer to about 280 milligrams of KOH per gram ofpolymer, more preferably greater than 6 milligrams of KOH per gram ofpolymer to about 100 milligrams of KOH per gram of polymer, with an acidnumber of from greater than 6 milligrams of KOH per gram of polymer toabout 70 milligrams of KOH per gram of polymer being most preferred.Generally, at higher acid numbers the resulting functionalizedpolypropylene exhibits higher adhesiveness to polar substrates and thusis more useful in combination with materials used in adhesives andsealants. Additionally, at higher acid numbers the functionalizedpolypropylene is useful as a compatibilizing agent or coupler when usedin blends of dissimilar materials, including polymer blends such as anylon and polypropylene blend. At higher acid numbers lower amounts offunctionalized polypropylene are generally needed for any of thesepurposes.

The functionalized polypropylenes herein are made from a polypropylenethat contains less than 20 weight percent of a comonomer. The comonomercan be any hydrocarbon monomer containing from 2 to 10 carbon atoms thatcan be copolymerized with propylene. Particularly useful is ethylenecomonomer.

The functionalized polypropylene herein can be blended with many othermaterials to serve as a compatibilizer, such as in blends with wood andpolypropylene. This type of blend typically contains about 30 weightpercent wood, about 67 weight percent polypropylene, and about 3 weightpercent functionalized polypropylene.

Additionally, the functionalized polypropylene of the present inventionis also useful to compatibilize other polar materials with the non-polarpolyolefin, especially polypropylene. Examples of other polar materialsinclude glass fibers, talc, mica and wollastonite.

The novel process according to the present invention for producingfunctionalized polypropylenes comprises:

(a) introducing a polypropylene either in molten form or solidparticulate form (e.g. powder or pellets) into an apparatus and meltingthe polypropylene if required to do so, at a temperature above themelting point of the polypropylene, preferably at a temperature of fromabove the melting point to about 230° C., and most preferably at atemperature of from above the melting point of the polypropylene toabout 200° C.,

(b) introducing into the molten polypropylene an amount of from about0.01 to about 99.99% by weight, preferably an amount of about 5 to lessthan 50% by weight, of the required amount of a free radical initiator,and mixing the free radical initiator with the polypropylene,

(c) introducing into the resultant mixture of polypropylene and freeradical initiator the entire required amount of functionalizing agent,preferably at a time of about 5 to about 180 seconds followingintroduction of the initital portion of free radical initiator, andmixing the functionalizing agent with the mixture of polypropylene andinitiator such that the functionalizing agent, the initial portion ofthe initiator and polypropylene are reacted to form a reaction mixture,

(d) introducing into the resultant reaction mixture the remaining amountof from about 99.99 to about 0.01% by weight, preferably an amount inexcess of 50% to about 95% by weight, of the free radical initiator,preferably at a time of about 5 to about 240 seconds after theintroduction of functionalizing agent into the mixture of polypropyleneand initial portion of initiator, and mixing the remaining amount ofinitiator with the previously formed reaction mixture in order to formthe desired functionalized polypropylene, and

(e) recovering the resultant functionalized polypropylene.

If desired, the remaining portion of the free radical initiator addedafter the functionalizing agent addition may be carried out in aplurality of zones. In each case the portion of the remaining freeradical initiator added is mixed to form an intermediate reactionproduct into which additional free radical initiator is added. Thepercent of the remaining free radical initiator that may be added ineach of the plurality of zones is between 1% and 99% by weight of theremaining free radical initiator added after the functionalizing agentaddition. Preferably, the number of additional free radical initiatorinjection zones is between 2 and 10.

The process according to the present invention functionalizes apolypropylene.

The process according to the present invention uses a free radicalinitiator to initiate the grafting of the functionalizing agent onto themolten polypropylene. Any free radical source can be used in the processof the present invention. However, peroxides are generally morepreferred. In the process according to the present invention, the sameor different free radical initiators can be used in either introductionpoint. The preferred peroxides are alkyl peroxides, more preferablydialkyl peroxides. Examples of suitable peroxides useful in the processof the present invention include ditertiary butyl peroxide, tertiarybutyl hydroperoxide, cumene hydroperoxide, p-menthane peroxide,p-menthane hydroperoxide and 2,5-dimethyl-2,5-di(t-butylperoxy)hexanewith ditertiary butyl peroxide and2,5-dimethyl-2,5-di(t-butylperoxy)hexane being most preferred. Otherexamples of peroxides suitable for use herein are tertiary butyl cumylperoxide, dicumyl peroxide, acetyl peroxide, propionyl peroxide, benzoylperoxide, tertiary butyl peroxy laurate, and tertiary butyl peroxybenzoate. Mixtures of peroxides are suitable for use in the presentprocess.

The functionalizing agent utilized in the present invention may be anyunsaturated monomer containing one or more carboxylic acid or acidanhydride groups, that can functionalize a polypropylene as definedherein. Examples of suitable functionalizing agents herein arecarboxylic acids such as acrylic and methacrylic acid, and acidanhydrides such as maleic anhydride. Further exemplary functionalizingagents suitable for use herein are unsaturated monocarboxylic acids andpolycarboxylic acids and cyclic acid anhydrides. Specifically includedherein are acids such as maleic acid, flumaric acid, himic acid,itaconic acid, citraconic acid, mesaconic acid, acrylic acid,methacrylic acid, crotonic acid, isocrotonic acid, and acid anhydridessuch as maleic anhydride and himic anhydride. Preferred for use hereinas the funtionalizing agent in the functionalization of thepolypropylene is maleic anhydride. Mixtures of functionalizing agentsmay be utilized in the present invention.

The process according to the present invention is conducted in acontinuous or batch process. Any continuous process can be used in thepractice of the present invention. However, stirred pot reactors withpowerful stirring mechanisms or screw extruders are favored, with screwextruders generally being more preferred. Twin-screw extruders are themost preferred screw extruders due to their ease of use and efficientmixing action. Screw extruders are also more preferred in that thepolypropylene is functionalized continuously with a shorter residencetime in the reaction zones. The use of a screw extruder in the processof the present invention aids in the production of functionalizedpolypropylenes.

The process according to the present invention is preferably conductedat a weight ratio of polypropylene to functionalizing agent of about 1to about 400, more preferably from about 2 to about 50, even morepreferably from about 2 to about 20.

The residence time of the polypropylene in a continuous reactor dependsupon the pumping rate of the polypropylene and the size (volume) of thereactor. This time is generally longer than three times the half life ofthe free radical initiator so that a second pass through the reactor isnot needed to obtain sufficient functionalization of the polypropylene.In a stirred reactor the residence time generally varies from about 5minutes to 1 hour, more preferably about 10 minutes to 30 minutes. In atwin screw extruder this time generally varies from about 0.45 to 5minutes, more preferably about 1 to 3.5 minutes at screw speeds of 100to 1500 revolutions per minute (rpm).

The molar ratio of polypropylene to free radical initiator used in thefunctionalization process according to the present invention in step(b), is preferably about 200 to 3500, and in step (d) is preferably amolar ratio of about 50 to 300.

The process according to the present invention is conducted at atemperature above the melting point of the polypropylene. Thistemperature is preferably from above the melting point to about 230° C.,more preferably at a temperature from above the melting point of thepolypropylene to about 200° C.

The process according to the present invention is generally conductedsuch that a vacuum is used after step (d) to remove volatiles from thefunctionalized polypropylene.

The invention will be more readily understood by reference to thefollowing examples. There are, of course, many other forms of thisinvention which will become obvious to one skilled in the art, once theinvention has been fully disclosed, and it will accordingly berecognized that these examples are given for the purpose of illustrationonly, and are not to be construed as limiting the scope of thisinvention in any way.

EXAMPLES

In the following examples the test procedures listed below were used inevaluating the analytical properties of the functionalizedpolypropylenes herein.

Acid Number—acid number was determined in accordance with ASTM D1386-83with the following modifications: A 0.05 N sodium hydroxide (NaOH) inmethanol solution was substituted for the 0.1 N aqueous solution ofpotassium hydroxide in ethanol and the sample size was increased from1-2 grams to 5 grams, and the weighing accuracy was changed from 0.001to 0.0001 grams.

Color—color was measured as “yellowness index” in accordance with ASTME313-73.

Viscosity is determined in accordance with ASTM D-3236 utilizing aBrookfield Model RVDV-II+digital Viscometer with a SC 4-27 spindle and aBrookfield Model 74R Temperature Controller set to 190° C., with thefollowing exceptions:

a. viscosity was recorded 20 minutes after beginning spindle rotation inthe sample;

b. only single measurements were taken for each sample; and

c. the rotational speed was 3 rpm.

The units are expressed as centipoise (cP).

Example 1

Pellets of Huntsman P4-026 polypropylene homopolymer having a melt flowrate of 1 g/10 min were fed into the inlet hopper of a Berstorff ZE 40A×55 L/D corotating twin screw extruder. Pellets were fed with avolumetric pellet feeder. The extruder temperature was maintained atabout 200° C. The polypropylene pellets were introduced at a rate ofabout 73 pound/hour (33.1 kg/hour). The extruder RPM was about 200. Theinitial portion of free radical initiator(2,5-dimethyl-2,5-di(t-butylperoxy)hexane) was injected into the moltenpolypropylene at a rate of about 0.16 pound/hour (0.07 kg/hour), 5% byweight of total initiator, and mixed with the molten polypropylene.Molten maleic anhydride was thereafter introduced into the mixture ofmolten polypropylene and initial portion of initiator at a rate of about14.4 pound/hour (6.5 kg/hour). The molten maleic anhydride was thenmixed with the mixture of molten polypropylene and initial portion ofinitiator such that a reaction mixture was formed. Into the resultingreaction mixture there was introduced2,5-dimethyl-2,5-di(t-butylperoxy)hexane initiator at a rate of about 3pound/hour (1.4 kg/hour), 95% by weight of the total initiator. Theresultant mixture was mixed such that the desired maleated polypropylenewas formed. Two zones of vacuum venting were used to remove volatiles,the first having 24 inches of mercury and the second having 27 inches ofmercury. The product was recovered by extruding the molten product intoa standard cold water stranding bath. The cooled strands weresubsequently chopped into pellets. The product was analyzed and found tohave the following properties: acid number of about 33.2 milligram ofKOH per gram of polymer; Brookfield Thermosel viscosity at 190° C. ofabout 27,000 cP; and a yellowness index color of 77.

Example 2

Pellets of Huntsman P5-012 random copolymer of polypropylene containing3 weight percent ethylene having a melt flow rate of 1.9 g/10 min werefed into the inlet hopper of a Berstorff ZE 40 A×55 L/D corotating twinscrew extruder. Pellets were fed with a volumetric pellet feeder. Theextruder temperature was maintained at about 177° C. The polypropylenepellets were introduced at a rate of about 65 pound/hour (29.5 kg/hour).The extruder RPM was about 300. The initial portion of free radicalinitiator (2,5-dimethyl-2,5-di(t-butylperoxy)hexane) was injected intothe molten polypropylene at a rate of about 1.5 pound/hour (0.68kg/hour), 43% by weight of total initiator, and mixed with the moltenpolypropylene. Molten maleic anhydride was thereafter introduced intothe mixture of molten polypropylene and initial portion of initiator ata rate of about 14.4 pound/hour (6.5 kg/hour). The molten maleicanhydride was then mixed with the mixture of molten polypropylene andinitial portion of initiator such that a reaction mixture was formed.Into the resulting reaction mixture there was introduced2,5-dimethyl-2,5-di(t-butylperoxy)hexane initiator at a rate of about 2pound/hour (0.9 kg/hour), 57% by weight of the total initiator. Theresultant mixture was mixed such that the desired maleated polypropylenewas formed. Two zones of vacuum venting were used to remove volatiles,the first having 26.5 inches of mercury and the second also having 26.5inches of mercury. The product was recovered by extruding the moltenproduct into a standard cold water stranding bath. The cooled strandswere subsequently chopped into pellets. The product was analyzed andfound to have the following properties: acid number of about 35.6milligram of KOH per gram of polymer; Brookfield Thermosel viscosity at190° C. of about 25,000 cP; and a yellowness index color of 105.6.

Example 3

Pellets of Huntsman P5-012 random copolymer of polypropylene containing3 weight percent ethylene having a melt flow rate of 1.9 g/10 min werefed into the inlet hopper of a Berstorff ZE 40 A×55 L/D corotating twinscrew extruder. Pellets were fed with a volumetric pellet feeder. Theextruder temperature was maintained at about 177° C. The polypropylenepellets were introduced at a rate of about 65 pound/hour (29.5 kg/hour).The extruder RPM was about 250. The initial portion of free radicalinitiator (2,5-dimethyl-2,5-di(t-butylperoxy)hexane) was injected intothe molten polypropylene at a rate of about 1.4 pound/hour (0.6kg/hour), 22% by weight of total initiator, and mixed with the moltenpolypropylene. Molten maleic anhydride was thereafter introduced intothe mixture of molten polypropylene and initial portion of initiator ata rate of about 20.6 pound/hour (9.3 kg/hour). The molten maleicanhydride was then mixed with the mixture of molten polypropylene andinitial portion of initiator such that a reaction mixture was formed.Into the resulting reaction mixture there was introduced2,5-dimethyl-2,5-di(t-butylperoxy)hexane at a rate of about 5 pound/hour(2.3 kg/hour), 78% by weight of the total initiator. The resultantmixture was mixed such that the desired maleated polypropylene wasformed. Two zones of vacuum venting were used to remove volatiles, thefirst having 22.5 inches of mercury and the second having 27.5 inches ofmercury. The product was recovered by extruding the molten product intoa standard cold water stranding bath. The cooled strands weresubsequently chopped into pellets. The product was analyzed and found tohave the following properties: acid number of about 47.2 milligram ofKOH per gram of polymer; Brookfield Thermnosel viscosity at 190° C. ofabout 27,000 cP; and a yellowness index color of 104.4.

It should be clearly understood that the forms of the invention hereindescribed are illustrative only and are not intended to limit the scopeof the invention. The present invention includes all modificationsfalling within the scope of the following claims.

I claim:
 1. A process for producing a functionalized polypropylenecomprising: (a) providing molten polypropylene in an apparatus, (b)introducing into the molten polypropylene a first amount of from about 5to less than 50 percent by weight of the total required amount of atleast one free radical initiator and mixing the first amount of freeradical initiator with the molten polypropylene to form a resultantmixture, (c) introducing into the resultant mixture of moltenpolypropylene and first amount of free radical initiator, at least onefunctionalizing agent comprising an unsaturated monomer containing oneor more carboxylic acid or acid anhydride groups, and mixing thefunctionalizing agent with the resultant mixture of molten polypropyleneand first amount of free radical initiator such that the functionalizingagent, the first amount of free radical initiator and the moltenpolypropylene are reacted to form a reaction mixture, (d) introducinginto the reaction mixture a remaining second amount of from about 95 toequal to or greater than 50 percent by weight of free radical initiator,and mixing the remaining amount of free radical initiator with thereaction mixture to form a functionalized polypropylene, and, (e)recovering the functionalized polypropylene.
 2. The process according toclaim 1 wherein the molten polypropylene is provided by meltingpolypropylene, in solid particulate form, at a temperature of from abovethe melting point of the polypropylene to about 230° C.
 3. The processaccording to claim 1 wherein the functionalizing agent is introducedinto the resultant mixture at a time of about 5 to about 180 secondsfollowing introduction of the first amount of free radical initiator. 4.The process according to claim 1 wherein the second amount of freeradical initiator is introduced into the reaction mixture at a time ofabout 5 to about 240 seconds following the introduction of thefunctionalizing agent.
 5. The process according to claim 1 wherein thefunctionalizing agent is maleic anhydride.
 6. The process according toclaim 1 wherein the weight ratio of polypropylene to functionalizingagent is from about 1 to about
 400. 7. The process according to claim 1wherein the apparatus is a screw extruder.
 8. The process according toclaim 1 wherein the free radical initiator is a peroxide.
 9. The processaccording to claim 8 wherein the peroxide is2,5-dimethyl-2,5-di(tertiary butylperoxy)hexane.
 10. The processaccording to claim 1 further comprising removing volatiles by at leastone vacuum from the functionalized polypropylene formed in step (d)prior to recovering the functionalized polypropylene.
 11. The processaccording to claim 1 further comprising maintaining the process at atemperature above the melting point of the polypropylene.
 12. Theprocess according to claim 1 wherein the remaining second amount of freeradical initiator is introduced using more than one injection.